Both CLIC4 and CLIC5A activate ERM proteins in glomerular endothelium

Abstract

The chloride intracellular channel (CLIC) 5A is expressed at very high levels in renal glomeruli, in both endothelial cells (EC) and podocytes. CLIC5A stimulates Rac1- and phosphatidylinositol (4,5)-bisphosphate-dependent ERM (ezrin, radixin, moesin) activation. ERM proteins, in turn, function in lumen formation and in the development of actin-based cellular projections. In mice lacking CLIC5A, ERM phosphorylation is profoundly reduced in podocytes, but preserved in glomerular EC. Since glomerular EC also express CLIC4, we reasoned that, if CLIC4 activates ERM proteins like CLIC5A, then CLIC4 could compensate for the CLIC5A loss in glomerular EC. In glomeruli of CLIC5-deficient mice, CLIC4 expression was upregulated and colocalized with moesin and ezrin in glomerular EC, but not in podocytes. In cultured glomerular EC, CLIC4 silencing reduced ERM phosphorylation and cytoskeletal association, and expression of exogenous CLIC4 or CLIC5A rescued ERM de-phosphorylation due to CLIC4 silencing. In mice lacking either CLIC4 or CLIC5, ERM phosphorylation was retained in glomerular EC, but, in mice lacking both CLIC4 and CLIC5, glomerular EC ERM phosphorylation was profoundly reduced. Although glomerular EC fenestrae developed normally in dual CLIC4/CLIC5-deficient mice, the density of fenestrae declined substantially by 8 mo of age, along with the deposition of subendothelial electron-lucent material. The dual CLIC4/CLIC5-deficient mice developed spontaneous proteinuria, glomerular cell proliferation, and matrix deposition. Thus CLIC4 stimulates ERM activation and can compensate for CLIC5A in glomerular EC. The findings indicate that CLIC4/CLIC5A-mediated ERM activation is required for maintenance of the glomerular capillary architecture.

Three Decades of Chloride Intracellular Channel Proteins: From Organelle to Organ Physiology

“…As shown in podocytes, it is involved in maintaining the structural integrity of cells (Edwards, ; Pierchala, Munoz, & Tsui, ) and stereocilia (Salles et al., ). CLIC4 is also co‐localized with ezrin, radixin, and moesin (ERM) proteins (Tavasoli et al., ). The channel activities of CLIC5 and CLIC1 can be modulated by cytoskeletal filaments (Singh, Cousin, & Ashley, ).…”

“…It is also reported to interact with ERM protein complexes and as playing a role in cellular architecture. The interaction of CLIC5 with the ERM complex in glomeruli is necessary to maintain the architecture of endothelial cells and podocytes (Pierchala et al., ; Tao et al., ; Tavasoli et al., ; Wegner et al., ). The predominant phenotype of clic5 –/– mice is inner ear dysfunction and hearing loss (Gagnon et al., ).…”

“…While these animals suffer from albuminuria and are susceptible to acute kidney injury, there is no effect on the functional recovery or fibrosis following injury (Edwards et al, 2014). CLIC4, in association with CLIC5, can mediate ERM activation which is required for maintenance of the glomerular capillary architecture (Tavasoli et al, 2016). Inhibiting CLIC4 expression increases β-cell survival, possibly caused by the increased cellular expression of Bcl-2, Bcl-xL and Bad phosphorylation (Patel, Ythier, Brozzi, Eizirik, & Thorens, 2015).…”

CLIC1 null mice demonstrate a role for CLIC1 in macrophage superoxide production and tissue injury

“…; Tavasoli et al. ). Whether as ion channels or as cytoskeletal regulators, CLICs clearly play a role in tubulogenesis of endothelial cells and of renal tubular epithelial cells (Ulmasov et al.…”

Emerging biological roles of Cl− intracellular channel proteins

“…Biochemical and colocalization studies suggest that, upon recruitment to the plasma membrane, both CLIC4 and CLIC5 function in a complex with ERM and/or actin-binding scaffold proteins, such as Na + /H + exchange regulatory factor 2 (NHERF2, officially known as SLC9A3R2) and the above-mentioned ERM proteins (Al-Momany et al, 2014;Berryman and Bretscher, 2000;Berryman et al, 2004;Ponsioen et al, 2009;Salles et al, 2014;Tavasoli et al, 2016a;Viswanatha et al, 2013). The association of CLIC4 and CLIC5 with the actin cytoskeleton and the finding that CLICs traffic between distinct subcellular compartments upon receptor stimulation (see below) strongly suggest a role for CLIC proteins in actin-dependent membrane trafficking.…”